Random access process of an unlicensed cell in a wireless device

1. A method comprising:

receiving, by a wireless device, a message indicating a maximum counter value;

performing a listen-before-talk (LBT) for transmission of a preamble for a random access (RA) procedure;

when a corresponding RA response is not received:

increasing a preamble transmission opportunity counter based on the LBT being performed;

increasing a preamble transmission counter based on the LBT being successful;

considering the RA procedure unsuccessfully completed in response to the preamble transmission counter reaching the maximum counter value; and

considering the RA procedure unsuccessfully completed in response to the preamble transmission opportunity counter reaching the maximum counter value.

2. The method of claim 1 , further comprising setting a preamble power parameter based on the preamble transmission counter.

3. The method of claim 2 , further comprising:

receiving a control order indicating the transmission of the preamble;

in response to receiving the control order:

resetting the preamble transmission counter; and

resetting the preamble transmission opportunity counter.

4. The method of claim 3 , wherein the control order is a physical downlink control channel (PDCCH) comprising a preamble index and a RA mask index.

5. The method of claim 2 , further comprising:

based on the LBT for transmission of the preamble indicating a clear channel, monitoring a control channel for the corresponding RA response during a RA response window; and

based on the LBT for transmission of the preamble indicating a busy channel, not monitoring the control channel for the corresponding RA response.

6. The method of claim 2 , further comprising:

based on the LBT for transmission of the preamble indicating a clear channel, starting a RA response window timer for monitoring a control channel for the corresponding RA response; and

based on the LBT for transmission of the preamble indicating a busy channel, not starting a RAN response window timer for monitoring the control channel for the corresponding RA response.

7. The method of claim 2 , further comprising based on the LBT for transmission of the preamble indicating a busy channel:

not starting a RAN response window timer for monitoring a control channel for the corresponding RA response; and

selecting a RA resource for transmission of the preamble in response to:

the preamble transmission counter being lower than the maximum counter value; and

the preamble transmission opportunity counter being lower than the maximum counter value.

8. The method of claim 1 , further comprising:

receiving a control order indicating the transmission of the preamble;

in response to receiving the control order:

resetting the preamble transmission counter; and

resetting the preamble transmission opportunity counter.

9. The method of claim 8 , wherein the control order is a physical downlink control channel (PDCCH) comprising a preamble index and a RA mask index.

10. The method of claim 1 , wherein the preamble transmission opportunity counter is configured to limit a time duration that the preamble is used for the RA procedure on a cell.

11. The method of claim 1 , further comprising:

transmitting, by a physical layer, the preamble if the LBT succeeds, otherwise dropping transmission of the preamble; and

receiving, by a MAC layer, a power ramping suspension indication from a physical layer when the transmission of the preamble is dropped due to a failure of the LBT.

12. The method of claim 1 , further comprising considering the RA procedure successfully completed when the wireless device receives the corresponding RA response.

13. The method of claim 1 , wherein the preamble transmission opportunity counter is configured to count a number of transmission opportunities of the preamble.

14. The method of claim 1 , further comprising selecting RA resources for the transmission of the preamble based on:

the corresponding RA response not being received;

the preamble transmission counter being less than the maximum counter value; and

the preamble transmission opportunity counter being less than the maximum counter value.

15. The method of claim 1 , further comprising monitoring a downlink channel for the corresponding RA response within a RA response window, the corresponding RA response comprising a preamble identifier of the preamble.

16. The method of claim 1 , wherein the message further comprises:

RA resource information elements of a RA channel (RACH) on a cell;

a RA response window information element; and

a maximum RA transmission counter information element.

17. The method of claim 1 , further comprising transmitting, by a physical layer, the preamble if the LBT succeeds, otherwise dropping transmission of the preamble.

18. The method of claim 1 , further comprising:

based on the LBT for transmission of the preamble indicating a clear channel, monitoring a control channel for the corresponding RA response during a RA response window; and

based on the LBT for transmission of the preamble indicating a busy channel, not monitoring the control channel for the corresponding RA response.

19. The method of claim 1 , further comprising:

based on the LBT for transmission of the preamble indicating a clear channel, starting a RA response window timer for monitoring a control channel for the corresponding RA response; and

based on the LBT for transmission of the preamble indicating a busy channel, not starting a RAN response window timer for monitoring the control channel for the corresponding RA response.

20. The method of claim 1 , further comprising based on the LBT for transmission of the preamble indicating a busy channel:

not starting a RAN response window timer for monitoring a control channel for the corresponding RA response; and

selecting a RA resource for transmission of a preamble in response to:

the preamble transmission counter being lower than the maximum counter value; and

the preamble transmission opportunity counter being lower than the maximum counter value.